绝缘栅型场效应管
信息来源：本站(zhan) 日期：2017-04-13
在(zai)结型(xing)场(chang)(chang)(chang)效(xiao)(xiao)(xiao)应管(guan)中(zhong)，栅(zha)(zha)极和沟(gou)(gou)(gou)道(dao)间(jian)的(de)(de)PN结是反向(xiang)偏(pian)置的(de)(de)，所(suo)以(yi)输入(ru)电(dian)阻很大。但PN结反偏(pian)时(shi)总会有一(yi)些(xie)反向(xiang)电(dian)流(liu)存(cun)在(zai)，这就限(xian)制(zhi)了(le)输入(ru)电(dian)阻的(de)(de)进一(yi)步(bu)提高(gao)。如果在(zai)栅(zha)(zha)极与沟(gou)(gou)(gou)道(dao)间(jian)用一(yi)绝(jue)(jue)(jue)缘层隔开，便制(zhi)成(cheng)了(le)绝(jue)(jue)(jue)缘栅(zha)(zha)型(xing)场(chang)(chang)(chang)效(xiao)(xiao)(xiao)应管(guan)，其输入(ru)电(dian)阻可提高(gao)到。根据绝(jue)(jue)(jue)缘层所(suo)用材料(liao)之不同(tong)，绝(jue)(jue)(jue)缘栅(zha)(zha)场(chang)(chang)(chang)效(xiao)(xiao)(xiao)应管(guan)有多(duo)种类(lei)型(xing)，目前应用最广泛(fan)的(de)(de)一(yi)种是以(yi)二氧化硅（SiO2）为绝(jue)(jue)(jue)缘层的(de)(de)金(jin)属一(yi)氧化物一(yi)半导体(ti)（Meial-Oxide-Semiconductor）场(chang)(chang)(chang)效(xiao)(xiao)(xiao)应管(guan)，简(jian)称MOS场(chang)(chang)(chang)效(xiao)(xiao)(xiao)应管(guan)（MOSFET）。它(ta)也(ye)有N沟(gou)(gou)(gou)道(dao)和P沟(gou)(gou)(gou)道(dao)两类(lei)，每(mei)类(lei)按结构(gou)不同(tong)又分为增(zeng)强型(xing)和耗尽型(xing)。
一、耗尽型MOS管
N沟道耗尽型MOS管和N沟道增强型MOS管的(de)(de)结构基(ji)本相同(tong)。差别在(zai)于(yu)耗(hao)尽(jin)型(xing)MOS管(guan)(guan)的(de)(de)SiO2绝缘层(ceng)中(zhong)掺有(you)大(da)(da)量的(de)(de)正离子，故(gu)在(zai)UGS= 0时(shi)，就在(zai)两个N十区(qu)之间的(de)(de)P型(xing)表面(mian)层(ceng)中(zhong)感应出大(da)(da)量的(de)(de)电(dian)子来，形成一定宽(kuan)度的(de)(de)导电(dian)沟道。这时(shi)，只要UDS＞0就会产生ID。对于(yu)N沟道耗(hao)尽(jin)型(xing)MOS管(guan)(guan)，无论UGS为正或负，都能控制(zhi)ID的(de)(de)大(da)(da)小(xiao)，并(bing)且不出现(xian)栅流。这是耗(hao)尽(jin)型(xing)MOS管(guan)(guan)区(qu)别于(yu)增(zeng)强型(xing)MOS管(guan)(guan)的(de)(de)主(zhu)要特点。
二、增强型MOS管
1．结构与符号
图Z0125是N沟道增强型MOS管的结构示(shi)意图和(he)符号。它是在一块(kuai)P型(xing)硅衬底(di)上(shang)(shang)，扩散两个高浓度掺杂的N+区，在两个N+区之间的硅表面上(shang)(shang)制(zhi)作一层很薄的二氧(yang)化(hua)硅（SiO2）绝(jue)缘(yuan)层，然后在SiO2和(he)两个N型(xing)区表面上(shang)(shang)分别引出(chu)三(san)个电(dian)极(ji)(ji)(ji)(ji)，称为源极(ji)(ji)(ji)(ji)s、栅极(ji)(ji)(ji)(ji)g和(he)漏极(ji)(ji)(ji)(ji)d。在其(qi)图形符号中(zhong)，箭(jian)头表示(shi)漏极(ji)(ji)(ji)(ji)电(dian)流的实际(ji)方向(xiang)。
2．输出特性曲线
N沟(gou)(gou)道(dao)(dao)(dao)(dao)(dao)增强型(xing)MOS管(guan)输(shu)出特(te)性曲(qu)(qu)线(xian)(xian)如图Z0127所示，它是UGS为不(bu)同(tong)定值(zhi)时(shi)(shi)，ID 与UDS之间关系的(de)(de)(de)(de)(de)一(yi)(yi)簇(cu)曲(qu)(qu)线(xian)(xian)。由图可见，各条曲(qu)(qu)线(xian)(xian)变化规律基(ji)(ji)本相同(tong)。现(xian)以(yi)UGS＝5V一(yi)(yi)条曲(qu)(qu)线(xian)(xian)为例来(lai)进行分析。设UGS＞VT，导电(dian)(dian)(dian)(dian)沟(gou)(gou)道(dao)(dao)(dao)(dao)(dao)已形成。当(dang)(dang)UDS= 0时(shi)(shi)，沟(gou)(gou)道(dao)(dao)(dao)(dao)(dao)里(li)没有电(dian)(dian)(dian)(dian)子的(de)(de)(de)(de)(de)定向运动(dong)，ID=0；当(dang)(dang)UDS＞0且较小时(shi)(shi)，沟(gou)(gou)道(dao)(dao)(dao)(dao)(dao)基(ji)(ji)本保持原状，表现(xian)出一(yi)(yi)定电(dian)(dian)(dian)(dian)阻，ID随UDS线(xian)(xian)性增大(da)(da) ；当(dang)(dang)UDS较大(da)(da)时(shi)(shi)，由于电(dian)(dian)(dian)(dian)阻沿沟(gou)(gou)道(dao)(dao)(dao)(dao)(dao)递(di)(di)增，使UDS沿沟(gou)(gou)道(dao)(dao)(dao)(dao)(dao)的(de)(de)(de)(de)(de)电(dian)(dian)(dian)(dian)位(wei)从漏(lou)端到源端递(di)(di)降(jiang)，所以(yi)沿沟(gou)(gou)道(dao)(dao)(dao)(dao)(dao)的(de)(de)(de)(de)(de)各点上(shang)，栅极与沟(gou)(gou)道(dao)(dao)(dao)(dao)(dao)间的(de)(de)(de)(de)(de)电(dian)(dian)(dian)(dian)位(wei)差沿沟(gou)(gou)道(dao)(dao)(dao)(dao)(dao)从d至(zhi)s极递(di)(di)增，导致垂直于P型(xing)硅表面的(de)(de)(de)(de)(de)电(dian)(dian)(dian)(dian)场(chang)强度从d至(zhi)s极也递(di)(di)增，从而形成沟(gou)(gou)道(dao)(dao)(dao)(dao)(dao)宽度不(bu)均匀(yun)，漏(lou)端最窄，源端最宽如图Z0126所示。随着UDS的(de)(de)(de)(de)(de)增加(jia)，漏(lou)端沟(gou)(gou)道(dao)(dao)(dao)(dao)(dao)变得(de)更窄，电(dian)(dian)(dian)(dian)阻相应(ying)变大(da)(da)，ID上(shang)升变慢 ；当(dang)(dang)UDS继(ji)续(xu)增大(da)(da)到UDS=UGS- VT时(shi)(shi)，近漏(lou)端的(de)(de)(de)(de)(de)沟(gou)(gou)道(dao)(dao)(dao)(dao)(dao)开(kai)始消失，漏(lou)端一(yi)(yi)点处被夹(jia)(jia)断(duan)；如果UDS再增加(jia)，将出现(xian)夹(jia)(jia)断(duan)区。这时(shi)(shi)，UDS增加(jia)的(de)(de)(de)(de)(de)部分基(ji)(ji)本上(shang)降(jiang)在(zai)夹(jia)(jia)断(duan)区上(shang)，使夹(jia)(jia)断(duan)部分的(de)(de)(de)(de)(de)耗尽层变得(de)更厚，而未夹(jia)(jia)断(duan)的(de)(de)(de)(de)(de)导电(dian)(dian)(dian)(dian)沟(gou)(gou)道(dao)(dao)(dao)(dao)(dao)不(bu)再有多大(da)(da)变化，所以(yi)ID将维持刚出现(xian)夹(jia)(jia)断(duan)时(shi)(shi)的(de)(de)(de)(de)(de)数值(zhi)，趋于饱和，管(guan)子呈现(xian)恒流(liu)特(te)性。
对于不同(tong)(tong)的(de)UGS值，沟道深(shen)浅也不同(tong)(tong)，UGS愈大，沟道愈深(shen)。在恒(heng)流区，对于相同(tong)(tong)的(de)UDS 值，UGS大的(de)ID也较大，表(biao)现为输出特(te)性曲(qu)线(xian)上移。
3．工作原理
绝(jue)缘(yuan)栅场效应(ying)管的(de)(de)导电(dian)机理是，利用UGS 控制"感应(ying)电(dian)荷"的(de)(de)多少来改变(bian)导电(dian)沟道的(de)(de)宽(kuan)窄(zhai)，从而控制漏极电(dian)流ID。若UGS＝0时(shi)，源、漏之(zhi)间(jian)(jian)不存在(zai)导电(dian)沟道的(de)(de)为(wei)增强型MOS管，UGS＝0 时(shi)，漏、源之(zhi)间(jian)(jian)存在(zai)导电(dian)沟道的(de)(de)为(wei)耗(hao)尽型MOS管。
图(tu)Z0125中(zhong)衬底(di)为(wei)(wei)P型(xing)(xing)半(ban)导体(ti)(ti)，在(zai)(zai)它的(de)(de)上(shang)面(mian)是(shi)一(yi)层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)SiO2薄膜(mo)、在(zai)(zai)SiO2薄膜(mo)上(shang)盖(gai)一(yi)层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)金属铝(lv)，如果在(zai)(zai)金属铝(lv)层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)和(he)半(ban)导体(ti)(ti)之(zhi)间加电(dian)(dian)压(ya)UGS，则金属铝(lv)与(yu)半(ban)导体(ti)(ti)之(zhi)间产生一(yi)个垂直(zhi)于(yu)半(ban)导体(ti)(ti)表面(mian)的(de)(de)电(dian)(dian)场(chang)，在(zai)(zai)这一(yi)电(dian)(dian)场(chang)作用(yong)下(xia)(xia)，P型(xing)(xing)硅表面(mian)的(de)(de)多数(shu)载(zai)流(liu)(liu)(liu)子(zi)-空(kong)穴(xue)受(shou)(shou)到排(pai)(pai)斥(chi)，使硅片表面(mian)产生一(yi)层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)缺乏载(zai)流(liu)(liu)(liu)子(zi)的(de)(de)薄层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)。同时在(zai)(zai)电(dian)(dian)场(chang)作用(yong)下(xia)(xia)，P型(xing)(xing)半(ban)导体(ti)(ti)中(zhong)的(de)(de)少数(shu)载(zai)流(liu)(liu)(liu)子(zi)-电(dian)(dian)子(zi)被(bei)吸(xi)引(yin)到半(ban)导体(ti)(ti)的(de)(de)表面(mian)，并被(bei)空(kong)穴(xue)所俘获而形(xing)成(cheng)负(fu)离(li)子(zi)，组(zu)成(cheng)不(bu)可移动的(de)(de)空(kong)间电(dian)(dian)荷层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)（称耗尽(jin)(jin)层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)又叫受(shou)(shou)主(zhu)离(li)子(zi)层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)）。UGS愈(yu)(yu)大，电(dian)(dian)场(chang)排(pai)(pai)斥(chi)硅表面(mian)层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)中(zhong)的(de)(de)空(kong)穴(xue)愈(yu)(yu)多，则耗尽(jin)(jin)层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)愈(yu)(yu)宽，且UGS愈(yu)(yu)大，电(dian)(dian)场(chang)愈(yu)(yu)强；当(dang)UGS 增大到某一(yi)栅源(yuan)(yuan)电(dian)(dian)压(ya)值VT（叫临(lin)界电(dian)(dian)压(ya)或开启电(dian)(dian)压(ya)）时，则电(dian)(dian)场(chang)在(zai)(zai)排(pai)(pai)斥(chi)半(ban)导体(ti)(ti)表面(mian)层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)的(de)(de)多数(shu)载(zai)流(liu)(liu)(liu)子(zi)-空(kong)穴(xue)形(xing)成(cheng)耗尽(jin)(jin)层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)之(zhi)后，就会吸(xi)引(yin)少数(shu)载(zai)流(liu)(liu)(liu)子(zi)-电(dian)(dian)子(zi)，继而在(zai)(zai)表面(mian)层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)内形(xing)成(cheng)电(dian)(dian)子(zi)的(de)(de)积(ji)累，从而使原来(lai)为(wei)(wei)空(kong)穴(xue)占多数(shu)的(de)(de)P型(xing)(xing)半(ban)导体(ti)(ti)表面(mian)形(xing)成(cheng)了N型(xing)(xing)薄层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)。由于(yu)与(yu)P型(xing)(xing)衬底(di)的(de)(de)导电(dian)(dian)类型(xing)(xing)相反，故称为(wei)(wei)反型(xing)(xing)层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)。在(zai)(zai)反型(xing)(xing)层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)下(xia)(xia)才是(shi)负(fu)离(li)子(zi)组(zu)成(cheng)的(de)(de)耗尽(jin)(jin)层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)。这一(yi)N型(xing)(xing)电(dian)(dian)子(zi)层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)，把原来(lai)被(bei)PN结高阻层(ceng)(ceng)(ceng)(ceng)(ceng)(ceng)隔(ge)开的(de)(de)源(yuan)(yuan)区和(he)漏区连接起(qi)来(lai)，形(xing)成(cheng)导电(dian)(dian)沟道。
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